A rectangular coil of length 0.12 m and width 0.1 m having 50 turns… | NEET 2015 (AIPMT)

Q20NEET 2015 · AIPMTMedium

Field of a Magnet & Magnet in a Uniform Field

A rectangular coil of length 0.12 m and width 0.1 m having 50 turns of wire is suspended vertically in a uniform magnetic field of strength 0.2 weber/m2. The coil carries a current of 2 A. If the plane of the coil is inclined at an angle of 30° with the direction of the field, the torque required to keep the coil in stable equilibrium will be

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Answer: (d)

$NIAB = 50 \times 2 \times (0.12 \times 0.1) \times 0.2 = 0.24\ \text{N m}$
The plane makes $30^\circ$ with $B$ , so the normal (moment) makes $60^\circ$ : $\tau = NIAB\sin 60^\circ = NIAB\cos 30^\circ$ .
$\tau = 0.24 \times 0.866 \approx 0.21\ \text{N m}$ , nearest option 0.20 N m.
So the answer is (d).

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